Interpretive Summary: In the colder parts of the United States, in late winter after disappearance of snow cover, red clover is often broadcast seeded into forage legume-depleted grass pastures to increase pasture forage quality. This method of establishment is referred to as frost seeding. However, in an estimated 30-40% of frost-seeded pastures in Wisconsin, USA the legumes fail to establish. Breeding for increased frost-seedability has not been attempted by plant breeders. This study measured the genetic basis of frost-seedability. Inheritance of frost-seeded seedling establishment traits is very low, suggesting that developing new varieties for this trait will be difficult. This study will help red clover breeders to optimize breeding programs to achieve selection gains for this frost-seeded establishment.

Technical Abstract:
In the colder parts of the United States, in late winter after disappearance of snow cover, red clover (Trifolium pratense) is often broadcast seeded into forage legume-depleted grass pastures to increase pasture forage quality. This method of establishment is referred to as frost seeding. However, in an estimated 30-40% of frost-seeded pastures in Wisconsin, USA the legumes fail to establish. In this study 40 red clover halfsib families from one breeding population and ten check populations were evaluated for spring frost-seeded establishment in three environments. Seedling establishment counts and plant heights were measured 3 months after frost-seeded planting. One of the three environments experienced a stand establishment failure. Narrow sense heritability estimates on a halfsib family basis for stand counts and heights were h2 = 0.07 and 0.63 respectively. Seedling counts were greatly affected by environment with micro-environmental effects contributing to low heritability. Additive by environment genetic variance was large, again leading to low seedling count heritabilities. These results suggest that it may be difficult to select for increased frost-seeded seedling establishment and that many test environments are needed to achieve genetic gains for this trait. In comparison, seedling height was very heritable with relatively small additive by environment genetic variances. The genetic correlation between seedling count and height using frost-seeded establishment was rA = 0.42.